In recent years, as a display, a liquid crystal display apparatus using a surface light source device has been remarkably widespread. In a liquid crystal display apparatus including an edge light-type surface light source device, for example, light emitted from a light source enters a light guide plate, and propagates through an inside of the light guide plate while repeating a total reflection on a light output surface (liquid crystal cell-side surface) of the light guide plate and a back surface thereof. A part of the light that propagates through the inside of the light guide plate allows a traveling direction thereof to be changed by a light scattering body or the like, which is provided on the back surface of the light guide plate or the like, and is output from the light output surface to an outside of the light guide plate. Such light output from the light output surface of the light guide plate is diffused and condensed by various optical sheets such as a diffusion sheet, a prism sheet, a brightness enhancement film, or the like, and thereafter, the light enters a liquid crystal display panel in which polarizing plates are arranged on both sides of a liquid crystal cell. Liquid crystal molecules of a liquid crystal layer of the liquid crystal cell are driven for each of pixels to control transmission and absorption of the incident light. As a result, an image is displayed.
Typically, the above-mentioned prism sheet is fitted into a casing of the surface light source device, and is provided close to the light output surface of the light guide plate. In a liquid crystal display apparatus using such a surface light source device as described above, the prism sheet and the light guide plate are rubbed against each other when installing the prism sheet or under an actual usage environment, and the light guide plate is flawed in some cases. In order to solve such a problem, a technology for integrating the prism sheet with a light source-side polarizing plate is proposed (Patent Literature 1). However, a liquid crystal display apparatus using such polarizing plate with which the prism sheet is integrated has a problem of being dark because front brightness is insufficient.
Further, a liquid crystal display apparatus using such surface light source device as described above involves a problem in that moire occurs owing to the regular structure of the prism sheet. To solve such problem, it has been proposed that the prism sheet be provided with a light diffusion layer. However, the use of a light diffusion layer having light diffusibility strong enough to dissolve the moire causes a problem in that the brightness of the liquid crystal display apparatus reduces. For example, Patent Literature 2 discloses (1) an optical member obtained by laminating a light-diffusible pressure-sensitive adhesive on one side of a polarizing plate and laminating a sheet member having a prism shape on the other side thereof, and (2) an optical member obtained by laminating a polarizing plate and a sheet member having a prism shape through a light-diffusible pressure-sensitive adhesive. Although the optical member of the item (1) can suppress the occurrence of the moire, the brightness and front contrast of the liquid crystal display apparatus become insufficient. The optical member of the item (2) cannot suppress the occurrence of the moire and makes the brightness of the liquid crystal display apparatus insufficient.